The present inventiion relates generally to compressors, including those used in refrigeration and HVAC applica- tions. More particularly, the present invention relates to a pressure equalization system and method for starting a compressor, such as scroll, rotary, or reciprocating compressor, while maintaining the condenser at a high pressure.
A standard refrigeration or HVAC system includes a fluid, an evaporator, a compressor, a condenser, and an expansion valve. In a typical refrigeration cycle, the refrigerant fluid begins in a liquid state under low pressure. The evaporator evaporates the low pressure liquid as the liquid absorbs heat from the evaporator, which raises the ambient temperature of the liquid and causes the liquid to undergo a phase change to a low pressure gas. The compressor draws the gas in and compresses it, producing a high pressure gas. The compressor then passes the high pressure gas to the condenser. The condenser condenses the high pressure gas to release heat to the condenser and undergo a phase change to a high pressure liquid. The cycle is completed when the expansion valve expands the high pressure liquid, resulting in a low pressure liquid. By means of example only, the refrigerant fluid used in the system might be ammonia, ethyl chloride, CFCs, HFCs, Freon(copyright), or other known refrigerants.
Typically, upon start up of a compressor, the pressure at both the suction port and the discharge port of the compressor is low. In operation, the compressor works the fluid to achieve a high pressure at the discharge port. However, when the compressor is no longer operating, the fluid on the high pressure side of the compressor (toward the condenser) flows back toward the low pressure side of the compressor (toward the evaporator) until a state of equilibrium between the formerly high and formerly low pressure sides is achieved. Thus, the pressure tends to equalize between the low pressure side and the high pressure side when the compressor stops operating. Such a system is inefficient because the refrigeration cycle requires energy at start up to create a high pressure in the condenser, which is needed to condense the fluid.
Another problem, specific to HVAC systems, is that it is difficult to efficiently achieve the high pressure start up, i.e. a start up where the pressures have not equalized, necessitated by seasonal energy efficiency requirements (SEER), a system used to rate HVAC systems. Start up components, such as a start capacitor and a start relay, are commonly used to overcome the differential pressure when the compressor needs to start with the unbalanced pressure in the system, i.e. the high pressure side of the system has a high pressure and the low pressure side of the system has a low pressure. These components achieve a high pressure differential start when the system is turned on. These components are rather expensive, however, and they produce high voltages and currents in the compressor motor upon start up.
Therefore what is needed is a system and method for equalizing the pressure in the compressor in order to start the compressor while maintaining a high pressure in the condenser and the high pressure portion of the system.
As explained in more detail below, the system and method of the present invention maintain a high pressure from a valve near the compressor discharge downstream to a condenser, but permit the pressure upstream of the valve to leak back toward the compressor suction until the pressure upstream of the valve has equalized with the low pressure side of the compressor. By high loading the pressure downstream from the valve and equalizing the pressure upstream from the valve, expensive and potentially dangerous start up components are eliminated. A benefit specific to HVAC systems is that the SEER rating of the system is not sacrificed.
The present invention is directed to a pressure equalization system for a compressor. The compressor has a compressor inlet for receiving a fluid at a first pressure from the evaporator and a compressor outlet for discharging the fluid at a second pressure to the condenser. The compressor is operable to compress the fluid from the first pressure to the second pressure. The system of the present invention includes a valve proximate to and in fluid communication with the compressor outlet and a bleed port upstream of the valve and in relatively low flow fluid communication with the compressor inlet. The valve has an open and a closed position. The valve is movable to the open position when the compressor is operating, to permit the fluid at the second pressure to flow through the valve. The valve is movable to the closed position when the compressor stops operating, to prevent backflow of the fluid at the second pressure through the valve toward the compressor inlet. The bleed port equalizes the pressure of the fluid contained in the compressor when the compressor stops operating.
In another embodiment, the present invention is directed to a pressure equalization system for a compressor having a high pressure side and a low pressure side, a compressor inlet for receiving a fluid at a first pressure, and a compressor outlet for discharging the fluid at a second pressure. The compressor is operable to compress the fluid from the first pressure to the second pressure. The system in this embodiment includes a container in fluid communication with the compressor, at least one valve operably disposed within the container, and a bleed port. The container has an inlet and an outlet, and either the inlet or the outlet of the container is connected to the outlet of the compressor. The container is divided into at least a first portion from the container inlet to the at least one valve and a second portion from the at least one valve to the container outlet. The valve is operably configured to permit the compressed fluid to flow through to the second portion of the container when the compressor is operating, and to prevent the compressed fluid in the second portion of the container from flowing back through the valve to the first portion of the container when the compressor stops operating. The bleed port connects the first portion of the container and the low pressure side of the compressor and is operably configured to bleed the compressed fluid from the first portion of the container to the low pressure side of the compressor when the compressor stops operating. The bleed port is further configured so that when the compressor is operating, the flow through the bleed port is relatively low, if not nonexistent. As a result, a negligible amount of fluid flows back to the compressor inlet, i.e. the low pressure side, when the compressor is operating.
Still another embodiment of the present invention is directed to a system to equalize fluid pressure between a first portion of a compressor at a first pressure and a second portion of the compressor at a second pressure greater than the first pressure upon the compressor not being in operation. The system includes a housing having a first and a second inlet for fluid and a first and a second outlet for fluid. The first and second inlets for a fluid are in fluid communication with the second portion of the compressor. The first outlet for a fluid is configured to permit flow of fluid from the system and the second outlet for a fluid is in fluid communication with the first portion of the compressor. The system further includes a chamber disposed within the housing. The chamber is in fluid communication with the first inlet, the second inlet, the first outlet and the second outlet. A piston is slidably disposed within the chamber between a first position and a second position, wherein the first inlet and the first outlet are in fluid communication upon the piston being in the first position and the second inlet and the second outlet are in fluid communication upon the piston being in the second position. The system also includes means for sliding the piston in the chamber between the first position and the second position. Finally, the means for sliding the piston in the chamber positions the piston in the second position upon the compressor not being in operation, thereby permitting fluid at a second pressure to flow through the second outlet to the first portion of the compressor to equalize pressure in the compressor.
A further embodiment of the present invention is directed to a system to equalize pressure between a first portion of a compressor at a first pressure and a second portion of the compressor at a second pressure greater than the first pressure upon the compressor not being in operation. The system includes a housing having at least one inlet for a fluid and first and second outlets for a fluid. The at least one inlet for a fluid is in fluid communication with the second portion of the compressor. The first outlet for a fluid is configured to permit flow of fluid from the system. The second outlet for a fluid is in fluid communication with the first portion of the compressor. The system further includes a chamber disposed within the housing being in fluid communication with the at least one inlet, the first outlet and the second outlet. The system also includes means for providing a fluid passageway from the at least one inlet to the first outlet upon the compressor being in operation and means for providing a fluid passageway from the at least one inlet to the second outlet upon the compressor not being in operation to permit a fluid at a second pressure to flow through the second outlet to the first portion of the compressor to equalize pressure in the compressor. The means for providing a fluid passageway from the at least one inlet to the first outlet comprising means for preventing fluid from entering the second outlet and the means for providing a fluid passageway from the at least one inlet to the second outlet comprising means for preventing fluid from entering the first outlet.
Yet another embodiment of the present invention is directed to a system to equalize pressure between a first portion of a compressor at a first pressure and a second portion of the compressor at a second pressure greater than the first pressure when the compressor is not in operation. The system includes a valve and a bleed port upstream of the valve. The valve is in fluid connection with the second portion of the compressor and has an open position permitting flow of fluid from the system upon the compressor being in operation and a closed position preventing flow of fluid through the valve upon the compressor not being in operation. The bleed port is in fluid communication with the second portion of the compressor and has a relief valve controlled by an operational feature of the compressor. The relief valve is in an open position upon the compressor not being in operation to permit flow of fluid through the bleed port to the first portion of the compressor to equalize pressure in the compressor, and the relief valve is in a closed position upon the compressor being in operation to prevent flow of fluid through the bleed port to the first portion of the compressor.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.